1,291 research outputs found
Giant capacitance of a plane capacitor with a two-dimensional electron gas in a magnetic field
If a clean two-dimensional electron gas (2DEG) with small concentration
comprises one (or both) electrodes of a plane capacitor, the resulting
capacitance can be larger than the "geometric capacitance" determined
by the physical separation between electrodes. A recent paper [1] argued
that when the effective Bohr radius of the 2DEG satisfies , one
can achieve at low concentration . Here we show that even
for devices with , including graphene, for which is effectively
infinite, one also arrives at at low electron concentration if there
is a strong perpendicular magnetic field.Comment: 6 pages, 5 figures; updated discussion about bilayer systems; added
discussion of fractional quantum Hall state
UnconstrainedMiner : efficient discovery of generalized declarative process models
Process discovery techniques derive a process model from observed behavior (e.g., event logs). In case of less structured processes, declarative models have notable advantages over procedural models. A declarative model consists of a set of temporal constraints over the activities in the event log. In this paper, we address three limitations of current discovery techniques: their unclear semantics of declarative constraints for business processes, their non-performative discovery of constraints, and their potential identification of vacuous constraints. We implemented our contributions as a declarative discovery algorithm for the Declare language. Our evaluations on a real-life event log indicate that it outperforms state of the art techniques by several orders of magnitude
Ultrastable lasers based on vibration insensitive cavities
We present two ultra-stable lasers based on two vibration insensitive cavity
designs, one with vertical optical axis geometry, the other horizontal.
Ultra-stable cavities are constructed with fused silica mirror substrates,
shown to decrease the thermal noise limit, in order to improve the frequency
stability over previous designs. Vibration sensitivity components measured are
equal to or better than 1.5e-11 per m.s^-2 for each spatial direction, which
shows significant improvement over previous studies. We have tested the very
low dependence on the position of the cavity support points, in order to
establish that our designs eliminate the need for fine tuning to achieve
extremely low vibration sensitivity. Relative frequency measurements show that
at least one of the stabilized lasers has a stability better than 5.6e-16 at 1
second, which is the best result obtained for this length of cavity.Comment: 8 pages 12 figure
Fyns Amt. Forurenet lokalitet nr. 485-20 - Tidligere maskinfabrik, Sortebrovej 26, 5690 Tommerup:Undersøgelser til vurdering af stimuleret in-situ reduktiv deklorering og kemisk oxidation ved oprensning af grundvandsforurening
JEM-X background models
Background and determination of its components for the JEM-X X-ray telescope
on INTEGRAL are discussed. A part of the first background observations by JEM-X
are analysed and results are compared to predictions. The observations are
based on extensive imaging of background near the Crab Nebula on revolution 41
of INTEGRAL. Total observing time used for the analysis was 216502 s, with the
average of 25 cps of background for each of the two JEM-X telescopes. JEM-X1
showed slightly higher average background intensity than JEM-X2. The detectors
were stable during the long exposures, and weak orbital phase dependence in the
background outside radiation belts was observed. The analysis yielded an
average of 5 cps for the diffuse background, and 20 cps for the instrument
background. The instrument background was found highly dependent on position,
both for spectral shape and intensity. Diffuse background was enhanced in the
central area of a detector, and it decreased radially towards the edge, with a
clear vignetting effect for both JEM-X units. The instrument background was
weakest in the central area of a detector and showed a steep increase at the
very edges of both JEM-X detectors, with significant difference in spatial
signatures between JEM-X units. According to our modelling, instrument
background dominates over diffuse background in all positions and for all
energies of JEM-X.Comment: 4 pages, 3 figures, A&A accepted (INTEGRAL special issue
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